Intramedullary (IM) nails have been used for fixation of fractures in long bones especially in the femur, tibia, and humerus bones. These nails are locked in position by locking screws at proximal and distal ends through holes provided in the nail. Due to the varying anatomy of the medullary canal, the nail often deforms when it is inserted inside the canal and often poses a challenge to the surgeon in correctly locating the distal holes. Typically X-rays are used to visualize the holes and the surgeon performs drilling free-hand. X-rays, however, are not ideal as they expose individuals to radiation, consume time, and may not be very accurate due to free hand drilling.
Aiming instruments that are capable of locating the distal holes without X-rays are known. Such an aiming instrument is shown and described in U.S. Publication No. 2013/0018381. Such instruments include a source unit that is inserted inside the cannulated IM nail and a sensor that needs to be positioned at a certain relative location with respect to the source unit in order to determine the location of the distal holes. Adjusting the sensor to the desired position, however, can be difficult.